1. Field of the Invention
The present invention relates to a device for transferring at least one toner image from a toner carrier belt onto a carrier material, whereby the toner carrier belt carries the toner image to be transferred and has a predetermined belt tension, and whereby the toner carrier belt, in a first operating status, is arranged close to the carrier material in the transfer area in order to transfer the toner image and, in a second operating status, is arranged at a predetermined distance from the carrier material in the transfer area in order to prevent a transfer of the toner image.
2. Description of the Related Art
Published PCT Application No. WO 98/39691 of the same applicant discloses a printer or copier for the performance-adapted monochromous printing and/or colored one-sided or two-sided printing of a recording medium. The device uses a transfer belt onto which toner images of different hues are superimposed onto one another in a first operating status. The overall toner image arising in this way by superimposition is subsequently transferred to the recording medium. In the collecting operating phase, the toner carrier belt is distanced from the carrier material so that a transfer of the sub-toner images is prevented. The transfer belt is arranged close to the recording medium when the collected overall toner image is transferred for transferring the overall toner image. The content of Published Application WO 98/39691, therefore, is incorporated by reference into the present patent application as disclosure content.
In the aforementioned device concept, the transfer belt therefore is removed from the carrier material at the transfer location given a stoppage of the printing operation and is moved again toward the carrier material when the printing continues. This back and forth motion must be smooth given the operating mode for multicolor printing, in particular, since a transfer printing process occurring at the same time between a photoconductor belt and the transfer belt for transferring a toner image is otherwise impairedxe2x80x94the toner image is blurred, for example. Traditional devices with belt tension devices are not without jerky movements in the toner carrier belt, however, so that belt tension changes lead to a lower printing quality.
German Patent A 42 10 077 discloses an image generation device having an electrostatic transfer device for a latent print image. A roller that can be pivoted via a mechanism serves the purpose of optionally causing contact between a transfer belt and a photoconductor drum.
German Patent A 41 39 409 describes a further image generation device having an electrostatic transfer printing device. A transport belt led via at least two rollers guides a print medium along a photoconductor drum. A latent print image thereby is transferred from the photoconductor drum onto the print medium.
An object of the present invention is to provide a device for transferring at least one toner image from a toner carrier belt onto a carrier material, whereby a high printing quality is obtained even given a back and forth motion of the toner carrier belt in the transfer printing area.
This object is achieved by a device for transferring at least one toner image from a toner carrier belt onto a carrier material, wherein the toner carrier belt carries the toner image to be transferred and has a predetermined belt tension, the toner carrier belt is held by a belt drive guiding the toner carrier belt through a roller device in the transfer printing area in which the toner image is transfer-printed onto the carrier material, the toner carrier belt, in a first state, is arranged close to the carrier material in the transfer printing area in order to transfer the toner image and, in a second state, is arranged at a predetermined distance from the carrier material in the transfer printing area in order to prevent a transfer of a toner image, and wherein the belt tension in the toner carrier belt is essentially the same in the first and second operating state.
Further advantages of the invention are realized by the belt tension also being the same in the transitional phase from the first operating state to the second operating state. In a preferred embodiment, the roller device is moved back and forth at least approximately perpendicular relative to the carrier material given a change of the operating states.
Preferably, the roller device has one single transfer printing roller which is moved back and forth at least approximately perpendicular given a change of the operating states, the belt drive has a stationary roller with a stationary rotational axis at both sides of the transfer printing roller, a movable compensation roller is respectively arranged between the stationary roller and the transfer printing roller, the respective distance between the rotational axes of the transfer printing roller and the compensation roller and the respective distance between the rotational axes of the compensation roller and the stationary roller remains constant in every operating state, and the diameters of the transfer printing roller, the compensation rollers and of the stationary rollers are of the same size. Specifically, the centers of the rotational axes of the transfer printing roller and the compensation rollers, as well as the centers of the rotational axes of the compensation rollers and the stationary rollers are connected to one another by rigid connecting-rod levers. The surface areas of the stationary rollers and of the compensation rollers may have contact with the toner carrier belt in both operating states and in the transitional phases. A movable cleaning roller of equal diameter may be arranged between the transfer printing roller and at least one of the compensation rollers, and the distance between the rotational axes of the transfer printing roller and of the cleaning roller, as well as the distance between the rotational axes of the cleaning roller and of the compensation roller remains constant in every operating state. The centers of the rotational axes of the transfer printing roller and of the cleaning roller, as well as the rotational axes of the cleaning roller and of the compensation roller are connected by rigid coupling elements.
As a preferred development, the rotational axis of the transfer printing roller is connected to a driving device which, in a linear motion, moves the rotational axis back and forth in an approximately perpendicular manner relative to the carrier material. The driving device may contain a switching eccentric. Alternatively, the rotational axis of the cleaning roller is connected to a further driving device moving the cleaning roller back and forth in a linear motion.
The toner carrier belt may be constructed to engage with a cleaning station or be removed from the cleaning station when the cleaning roller is moved back and forth.
The roller device of one embodiment is driven during its back and forth motion by the control surface of a rotating radial cam, at least one compensation roller is moved back and forth during the rotation of the radial cam, and the difference in length of a belt backlash, given the motion of the roller device, is compensated by the motion of the compensation roller. The roller device may contain two transfer printing rollers which are simultaneously moved back and forth by the control surface of a radial cam, each transfer printing roller having one compensation roller allocated to it, which is moved back and forth by the control surface of a radial cam. The transfer printing rollers and the compensation rollers that are respectively allocated to them are driven by the same radial cam. The radial cams are symmetrically rotated in preferred embodiments, or the radial cams can be asymmetrically rotated.
In one embodiment, the roller device can be moved in the direction of a guide bar, two tension rollers are symmetrically arranged relative to the guide bar, whereby the tension rollers are respectively connected by swivel arms to one end of the guide bar and by respectively one connecting rod to a sliding piece, which can be moved back and forth on the guide bar, and the tension rollers are charged with equal forces for pressing against the toner carrier belt.
A spring pressing against the sliding piece can be arranged on the guide bar. The roller device contains two transfer printing rollers that are symmetrically arranged relative to the guide bar. The belt drive may have two stationarily arranged deviation rollers for the toner carrier belt at both sides symmetrically relative to the center line of the guide bar, and the deviation rollers are of equal diameter. The belt drive of the preferred development does not contain additional tension elements apart from the two tension rollers.
In the first and second operating states, the belt tension in the toner carrier belt is inventively kept constant. The length of the toner carrier belt does not change as a result and belt tension spikes are prevented. Given simultaneous transfer printing of a toner image onto the toner carrier belt at a second transfer area, the environmental conditions in this transfer area remain constant and a high printing quality can be obtained as a result of the constant belt tension.
Advantageously, the belt tension in the toner carrier belt also remains the same in the transitional phase from the first operating state to the second operating state and vice versa. This means that the transport motion of the belt can also be maintained during this transitional phase without reducing the quality given simultaneous transfer printing of a toner image onto the toner carrier belt.
A transfer belt is to be preferably provided as a toner carrier belt, whereby a toner image is transferred, in a transfer printing process, from a toner image generation device, such as a photoconductor drum or a photoconductor belt, onto the transfer belt.